Kostmann syndrome : a clinical and pathophysiological study

Abstract

Kostmann syndrome or severe congenital neutropenia (SCN) is a rare disease, usually diagnosed during the first months of life, characterized by extremely low levels of neutrophils in the peripheral blood, a maturational arrest of the myelopoiesis in the bone marrow and severe bacterial infections. The purpose of this project was to improve the understanding of the clinical course and the pathophysiology of autosomal recessive SCN.

Rolf Kostmann presented six patients with autosomal recessive inherited congenital agranulocytosis in a kindred from Överkalix, Norrbotten, Sweden in his thesis 1956 and another ten patients in a review 1975. Today, four patients from this kindred are alive. Initially we described the survivors from a clinical perspective along with a review of the literature regarding the syndrome (I). This review of patients and literature resulted in a number of questions for further investigation. One such question was why the patients still have recurrent infections, particularly periodontal infections, despite normal absolute neutrophil counts (ANC). Functional studies of neutrophils in granulocyte colony-stimulating factor (G-CSF) treated patients with SCN had so far not revealed any major abnormalities. In Paper II we analyzed antibacterial peptides in the patients' neutrophils and found a deficiency of the peptide LL-37 and decreased levels of alpha defensins. No LL-37 could be detected in the saliva of the patients. One of the patients, who had undergone a bone marrow transplantation, had almost normal concentrations of LL-37 and normal dental status, indicating that the degree of peptide deficiency correlated with the severity of the periodontitis. The in vitro efficiency of antibacterial peptides is well documented and we therefore propose an in vivo role of antibacterial peptides in the prevention of bacterial infections in man generally and in patients with SCN in particular.

To further elucidate the underlying mechanisms we wanted to see if the maturation block of the myclopoiesis is due to excessive apoptosis (III). We studied apoptosis in specimens from bone marrow aspirates and biopsies. Prior to the initiation of G-CSF therapy there was an increased amount of apoptotic bodies and decreased levels of the anti-apoptotic protein Bcl-2, and both these findings normalized after the initiation of G-CSF treatment. We also found increased apoptosis in myeloid progenitor cells; especially CD33+ cells were prone to apoptosis. Apoptotic assays on CD34+ and CD33+ cells showed increased release of cytochrome c from mitochondria, which was partially reversed by G-CSF. The results indicate a role for mithocondria-dependent apoptosis, and provide an explanation for the beneficial effect of G-CSF, in patients with Kostmann syndrome. We also compared the efficacy of two different recombinant human G-CSF (rHuG-CSF) preparations in 7 patients with SCN (IV). The biological activity has been suggested to be higher for the glycosylated (lenograstim) than for the non-glycosylated (filgrastim) preparation. We could not confirm this advantage; on the contrary, filgrastim treatment resulted in significantly higher levels of ANC. However, we could not demonstrate any difference in clinical efficacy in our limited patient material. In Paper V we describe the odontological experience from patients belonging to the family Kostmann originally described, particularly from the perspective of deficiency of antibacterial peptides in the neutrophils of these patients. Prior to G-CSF treatment, some patients developed aggressive periodontitis already at preschool age. The dental status improved on G-CSF treatment, but the patients still suffer from periodontal disease. Professional dental care is still important in patients with SCN, despite treatment with G-CSF and normal levels of neutrophils.